Duct forming core



Aug. 27, 1963 R. E. sM'lTH 3,101,519

DUCT FORMING CORE Filed Nov. 29. 1961 1@ QOBEQTL. KAHNjZ@ desired length and sectionalarea.

United States Patent O lice 3,101,519 DUCT FORMING CORE Robert E. Smith, Dayton, Ohio, assigner toThe Flexicore Co., Inc., Dayton, Ohio, a corporation of New York Filed Nov. 29, 1961, Ser. No. 155,644 Claims. (Ci. 25-128) v [This invention relates to a duct forming core for del iining ducts during the casting of concrete slabs.. The

lslabs in which these ducts are provided are cast in lengths i indifferent success.

riuid tight tubular metal `members which were expanded 3, l l ,5 19 Patented Aug. 27,v 1963 sary that even a metal core will require some means to ,properly position it along the length thereof injthevcasting mould. However, the -greater stiffness `of a rigid core will make it unnecessary to space.`saidmeans asclosely as with fabric cores. Y M A [Attempts have been made to use'metalrcores, with Some metal cores have consisted/of under high pressure. During casting, the pressure is mainl0l ranging from about Ztl-feet to as much as 50 or k6() feet, -f Awhile the height of the slab is generally small in 'cornparison to the length thereof. As a rule, the widthof the slab may also be small in comparison to the length, but the width is generally greater than the height or depth of the slab. In slabs of. this character, it is advantageous to provide lducts of circular or non-circular cross section.`

yextending the full length of theslab Such ducts not only save on concrete mix, but impart desirable characteristics 'to the slab as a Whole. v n

For many years, slabs of this type, such as, for exarnple, disclosed in United States Patent No. 2,299,111, have been manufactured with ducts having a generally circular cross section. The cores for forming such ducts have conveniently been ofrubberized 'fabric or similar material arranged to berexpandable. Such cores are convenient because of their deflated condition they can' be folded as they are pulled out and can bestored Without taking too much room'. vIn use, suchpcores are expanded by compressed air and'serve to define a duct having the One disadvantage of such'fabric cores isbased upon i the fact that the cores when iniiated do not have substantial rigidity. A core must lbe positioned at frequent intervals along the .length thereof to` maintain it accurate- -ly within the casting mould. In casting long slabs, it is necessary that a duct be true and be accurately located throughout the entire length of the slab. Unless such a flexible fabric core is positioned at intervals of, say every two or three feet, it is ditlicult to maintain the length of the core in desired predetermined position.

This invention provides a core construction, principal- `ly of metal or stiff material, having substantially greater tained in the core. To remove the-core, itis necessary to relieve the,l pressure whereupon' the core contracts and pulls awayfrom -the concrete enoughso that the core maybe pulled out lengthwise. A f l f 5- .A metal vcore as described above Vis -not desirable for the reasonthat vhigh pressures require costly'equipment and'limit the pressure medium within the core to a liquid `in order toavoid danger. yFurthermore the corewexpan- `sion is microscopic. Another serious drawback Vto such a. core resides in the fact that the entire coremust be strength and stiffness than a tubular fabric core, as previously described. A rigid core for forming ducts has some` substantial advantages over a core made of textile matei rial or rubberized fabric. As an example, the metal or v rigid vmaterial constituting the core transmits efhciently high frequency vibrations generally used in compacting the mix in the casting form. 4High frequency vvibratory energyl is generally relied upon for compacting the mix and permits the use of a drier mix than might normally be the case.

, IIt is understood of course, ,that aminimum amount of water must be provided for setting the concrete. How-v ever, beyond this minimum amount of water, additional water is unnecessary for setting and does not provide any advantages. The drier the mix, the more quickly the concrete will cure, andthe stronger the finished material.

.Hence a rigid tubular member, such as of metal, for providing a duct is highly desirable because of the improved high frequency compacting action. )In particular, .the mix can be poured over the core and into the casting form much faster since .the high frequency energy reected from the side of a core causes the mixV tovllow past the core and settle, to the forrnbottom quicker.

In addition to the above, metal may bemade thick enough so that a long rigid core can `be quite stiff in comparison 4to cores of rubberized fabric. It is true that a rigid core with no intermediate positioners is not stiff enough to be properly located between ends when lengths of 30 or more feet are considered. It is thereforeV necespulled out -as a uni-t.

'tight against-high pressure., l. l It has also been proposed to use metal cores -in' the form of a slotted tube having a rubber mouldinggwedged between the edges and maintaining the core in expanded condition. To remove such Aa core from a cured casting, a rope attached to the moulding at the far ordead end of the coreis pulled to strip the moulding forcibly from v .the edges of the metal core, whereupon the naturalspring of, `the. metal results in the core contracting tofpermit A*withdrawal thereof. A drawback-to 'this is,;the expense .Y

"due yto the requirement that the moulding be put into Yposition foreach casting operation, witlrtherope positioned in the coreinside from the `dead `bulkhead'cnd toward `the live bulkhead end so that the'rope may be Vpulled forgstripping.l Such a procedure-,can betolerated for short `cores of the Vorder of 20 or 25 feet,'and even .them the time consumed makes such a procedure expensive.- For long cores of the order of-:50or .60 feet, such a procedure becomes so expensive'as to be prohibitive. -In addition, there is substantial wear'and tear-,on the moulding. i

This invention provides av'rigid core construction .lutilizing a slotted rigid tube and having an inatable exible ,tubefor expanding the metalcore member. f'

The new core involves a strong, resilient duct forming core member, preferably Iof metal, and having a 'continuous slot otr openingy along the length thereof. Ilhe core member is preset so that it tendsto Iassume a normal, 'free contracted shape, which, shape is designed tombe somewhat smaller laterally thanthejnal duct shape lto be moulded.

In accordance with the present invention, a laterally expandable, elastietwbul-ar airtight member is provided along the full length lof the core member i the saine and making a-complete conewassernbly there.-

with. vMeans aire provided -foir utilizing the laterally vexbly is forcibly separated fnom rthe adjacent surface ofthe.

concrete. This permits the en-tine core 'assembly' tdbe The new core may rbe easily adapted for various duct shapes, either circular or 'non-circular, symmetrical "vor otherwise. l

f inonder that the inventionV may be under'ste'od, refer` ence rwill now be made to the drawings whereint.

FIGURE 1 is a transverse section of a embodying the present invention.

FIGURES 2 and 3 are transverse sections of modied core assemblies embodying the present invention.`

p FIGURE 4 is a section along line 4-4 of FIGURE l.

core assembly Duct forming core member `lil may be tot steel or other the ylongest slab-to be cast in a slab casting mould. In 4 practice, the duct forming core member will be about one or two neet longer than the longest casting, since the duct formilplg core member must project through apertures or openings in bulkheads in a casting form. Thus such a core can be as long as 62 feet in length. Cores in tandem however, may be used desired. The casting norm disclosed in United States Patent No. 2,614,309, issued 'on October 21, 1952, may be used `in conjunction with these cores.

Duot forming ooremember It) may have any desired ycross sectional shape and may be circular, elliptical, rectangular, polygonal, or any irregular shape. lFor simplicity, duct forming core member lll is here illustrated as having a generally elliptical shape. This, however, is-

exemplary.

Duct forming clore member lil is tubularfor the length thereotand has a longitudinal slot lfor opening extending `the. full length of the tube. As illustrated here, duct formal-'dg core memberfltl has 'edges l1 and l2 dening the slot or zopening extending the full. length thereof.v

`For. convenience, edges 1I and I2 may extend straight along the'length of the core. The location or orientation off the core slot with reference to the transverse shape of the core member may be Varied. For example, FIGURE l illustrates the slot or opening between edges ld and l2 as being disposed substantially at the end or" the long diameter of the core member. This slot, however, may Abe located elsewhere.

The transverse dimension of the slot between edges 11 and 12 of the tubular core can generally be of the order of about 1/2" in the normally contracted position. In the expanded condition of the c'ore member, this slot width may increase from about 1/2" up to as much as 1" depending upon hoW much lexpansion is desired.

The length of the long diameter in a practical core may range from about live or six inches to as much as 15 or 20 inches, or even more if desired. The length of the short diameter may range from as little as about two inches toas much as 12 inches or more.

In the core member illustrated in FIGURE l, the

,'metal, such as steel, making Vup core member I0 may conveniently be` bent back at portions Il and l2 to provide inside layers I4 Iand l5 extending transversely toward portion 16 of the core member which is at the end I of the longrdiameter removed from edge portions Il and 12. Portion 16 of the core member may be considered as the hinge p'ortion, while inner layers '14 and 115' of the metal are useful for reinforcing the core member and stiiening the same against :being distorted during the springing oct the core member.

In the particular form of the invention illustrated in FIGURE 1 where the transverse shape is such that one transverse dimension is longer than another transverse dimensiom'it is possible to dispose core member 10 resilient tube 20 of rubber or other resilient material. Tube 20 should be and in practice may `have a thickness of about 1A", but it may be smaller or somewhat larger. As a rule, the air pressure within tube 20 may -go up as high `as 4()1 or 50 pounds per square inch, but will generally be in the neighborhood of 201 pounds per square inch. The actual air pressure required will I depend upon the thickness of metal member d0 and the .posed overmetal members 28 and 29.

stiffness thereof and the amount of expansion of transverse dimensions. Tube 20 may be of any suitable material which will hold air and can withstand some wear and tear.

No `attempt is made to show proportions 0f the slot between edge portions Il and I2 with respect to the transverse dimensions of the entirewcore assembly. In practice, Ias pointed out previously, the distance between edge portions Il and I2 will normally be about 1/2 and can expand up to as much as l. Elastic tube 20 may be sulcently stift` vso that there Will be little, if any, tendency for elastic or resilient tube Ztl to bulge or blow out through the slot. 2i) to project .through the slot may result in `a slight bulge, which bulge in practice, may be relied upon as part of the ductdening surface. However, moulding 23 of rubber or similar resilient material can be provided for closing lthe slot in the duct forming `core to lock inner tube 20 within core member lll. Moulding 23 has slots 24 and v2 therein for `accommodating edge portions 1I and 12 of the core member. Preferably, moulding 23 is Wide enough transversely of the length of the core so that slots 24 and 25 can be deep enough to permit edge portions Il and l2 of the `core metal to move from a contractedto an expanded position landstill remain in the slots.

y Referring to FIGURE 4, a simple means for closing theends of tube 2li is illustrated. Tube 20 can be a simple rubber .tube of generally uniform diameter having any desired length. 'I'he end portions of tube 20 extend beyond core members l@ if desired and are disi Metal members 28 and 29 :are preferably of the same elliptical shape as core member lil except that the transverse dimensions of metal members 2S and 29 are sullciently smaller than that of core member It?, so that even with the thickness of elastic tube 2d, the outside dimensions of the end portions of the entire assembly will be Somewhat less, and at the most, will be no greater than the tranverse dimensions of core member I0 when expanded. vIt desired, core member l0 may actually extend over metal portions 28 and 29. Metal members 23 and 29 have grooves 3) yformed therein, and at these grooves, metal bands 3'Ia1c tightly stretched over the outside of tube Ztl to lock the tube in position. Metal members 23 and 29 are generally similar except that 28 has iitting 33 for permitting `air to 4pass in or out while metal member 29 simply provides a 'dead end for the assembly. Grooves 30 for accommodating bands 3l. 4are deep enough so that fixtures 28 and 29 with the tube wall around the same and with the metal bands can be pulled through an opening in the bulkhead for accommodating core member 10.

inasmuch as the core 'assemblies will generally 'be pulled out of the :casting mould and sla'b in one direction at all times, it is possible to have only one of the end portions, `for example, the rear end portion containing tting 29, small enough to pull through the bulkheads. The front end containing `fitting 23 can be as large as desired in such case, since itwill 1always be outside of the *bulkhead at the live `end of thev casting form and will never have to be pulled through anopening shaped to t core member lil. Core member 1i) is preferably long enough to extend between bulkheads `and is preferably somewhat longer to extend up `a bit beyond the bulkheads on both ends so that there Will be no trouble in pulling thecore assembly out of the casting. If core members Iii extend through the bulkhead, it will be understood that the openings in the bulkhead will have to be shaped to accommodate the core memberfin its expanded position.

`Fitting 33 preferably `contains a valve similar to those used in automobile tires so that tube 20 may be lled with `compressed air that maybe retained for any desired length of time and may thereafter be deflated when desired.`

In orderl to'use the fcore assembly illustrated in FIG- URES 1 and 4, it will be necessary to dispose the core assembly in va casting form that is ready to receive the Some tendency for the inner tube 4to vibration. The vibration functions to aid the liow of the mix into position. The metal making up core member will readily transmit such vibrations yalong the length of the mould. The metal of core member 10 functions as an excellent transmitter and reflector of such vibratory energy and permits the use of concrete having -a slump of less than three inches and also speeds Ithe liow of the mix into the mould.

Preferably, though not necessarily, before concrete mix is poured into the casting mould, air is introduced into elastic tube to cause this to expand laterally. rl'Fhis may however, be done after the mix has been added. In any case, the lateral expansion of tube 20 exerts force against the inside wall of core member 10 and results in the core member being sprung outwardly. The expansive force will result in increased separation of edge portions 11 and 12. This will have the effect of increasing the short diameter of the ellipse by a suitable amount, such as, for example, a quarter of an inch. At the same time, there will be a tendency for core member l()l to be straightened out somewhat and thus increase the long diameter of the ellipse. 'Ilhis latter Itendency will be reinforced by the tendency of tube 20 to push moulding 23 outwardly somewhat. The change in dimension need not be great and can be as little as about 1A The compressed air in tube 20 is maintained there While the casting mould with its load of cement mix is curing. The curing is generally eliected in a steam room for a period of eight or ten hours at a temperature of 140 to 150 When the curing is done, the casting mould and the contents lare removed from' the curing room. 'Ilhe duct forming assembly is deflated by letting air out of tube 20. The entire core assembly may now be pulled out from the casting through one bulkhead, Iafter which the finished `casting may be removed from the casting mould.

Instead of having an inflatable tube filling the entire space within core member 10, it is possible to use a substantially narrower or smaller tube insofar as transverse dimensions are concerned and yconcentrate the expansive -force upon the portions of lthe core member adjacent the slot. For example, there is shown in FIGURE 2 a modification wherein core member 10 has the same general construction as core member 10 of FIGURE l except that substantially rigid operating members 35 and 36 .are disposed within core member 10 and `attached to edge or slot forming Iportions of 11 and 12. Inliatable tube 20 is disposed Within members 35l and 36. Operating members 35 and 36 do not completely form an enclosure for inilatable tube 20'.

In the modification illustrated in FIGURE 2, air pressure inside of tube 20' will result in creating a force tending to spread edge portions 11' and 12 apart. In this modication, tube 20 is so much smaller laterally than core member 10' that there will be no difficulty with regard to fittings at the ends of the tube. Thus, generally circular metal fittings can be used to form vclosures at the ends of tube 20 and there would generally be no trouble in extending tube 20 and the littings through the bulkheads. As a rule, the bulkheads in the casting form will 'have an opening therethrough for accommodating duct forming member 10 in its expanded condition.

In the construction illustrated in FIGURE 2, the operating members 35 and 36 can Ibe as rigid as desi-red.

Referring now to FIGURE 3, a modification Igenerally similar to FIGURE 2 is illustrated, except that in FIG- URE 3, the slot along member 10" is at the end of the short diameter rather than the long diameter as in FIG- URE 2. In FIGURE 3, operating member 40 extends l continuously to form a complete enclosure for elastic tube f 6 20". Member 40 need notnecessarily be of metal in FIGURE 3 and coul-d be of some strong non-stretchable but flexible material such as heavy canvas or reinforced plastic. iIn such case, the tendency of tube 20'. to expand would be limited and the expansive force of tube 20"' would 'be directed toward spreading the edges of the metal making up core member 10". If operating member 40 is of metal, then it should be no heavier and preferably should be more flexible than core member 10". l

The modification las illustrated in FIGURES 2 and 3 using a relatively small diameter inflatable tube and applyling the expansion force directly to the slot edges of the core member may be used for core members having shapes `other than elliptical. `In particular, a core member having a transverse generally circular shape may be used. In such case, a relatively small inflatable tube opcrates only on a small part of the core defining member. The rigidity of the' metal making up the duct forming core portion can be relied upon for use in pulling the metal away from the concrete side wall even if the lforce is only applied adjacent the slot. So long as there is some change in the lateral dimensions of metal member 10 or the corresponding metal members in FIGURES 2 and 3, it will suffice to pull the metal away from the concrete even if the movement is quite small. So long as the bond between the metal and the concrete is broken, there will be little trouble in. removing the duct forming core assembly. With regard Ito the moulding portion which may contact the con-crete, this ywill be of rubber or plastic, to which concrete does not adhere. The exact shape of operating members `35 and 36 of FIGURE 2 is not -too importa-nt.

With reference to FIGURE 3, member l40 is of metal and can be quite thin. This metal is subjected to a tensile Iforce. The non-circular shape of portion 40 in yFIGURE 3 is provided to cause tube 20 to stretch and open up the slot forming portions of 11" and i12.

What is claimed is:

1. A core assembly for defining a duct throughout the length of a concrete slab during casting, said core assembly having a length `great in comparison to any transverse dimensions thereof, said core assembly including an elongated slotted tubular metal member, said member being straight and long and having a transverse shape which remains uniform throughout the active length thereof and in transverse section defines an area which is almost but not `completely surrounded by a section of said member so that -said member has a lgenera'lly tubular shape with a `slot extending the lfull length thereof, a moulding covering said slot and tending to keep said slo-t closed even though the slot width is increased by deforming said member, an airtight, flexible tube 'within said member and having the property of lateral expansion in response to lluid pressure, and laterally expandable means disposed over said Iliexible tube and coupled to said slotted tubular member only at regions adjacent the slot, said air-tight tube exerting its expansive force directly against the laterally expandable mean-s which in .turn exerts force upon slot bordering regions `of said tubular slotted member to widen .the slot and spread the slotted member, said tubular member having suli'icient elasticity to contract and restore the slot tonormal width in the absence of any expansive [force in said air-tight tube whereby said air-tight tube can have substantially smaller lateral dimensions than said slotted tubular member. l

j 2. A core assembly for defining a duct throughout the length of a concrete lslab during casting, said core assembly having a length great in comparison to any transverse dimensions thereof, said core assembly including an elon- .gated slotted tubular metal member, said member being straight and long and having a transverse shape which remains uniform throughout the active ylength thereof and in transverse section defines an area which is almost but not completely surrounded by a section of 4said member t 7 so lthat said member has a Agenerally tubular shape with a slot'extending the full length thereof, means attached to said tubular member at the interior thereof at regions adjacent the slot defining edges for providing an elongated tubular laterally expansible enclosure and an airtight resilient tube within 'said last named enclosure for creating force in response to air pressure for spreading said tubular member to increase the normal slot width, said tubular member having Iinherent elasticity and tending -to return to its vnormal condition providing a normal slot Width upon the release of said air in said tube.

3. The construction according to claim 2 Iwherein said slotted tubular metal member is of steel having a thickness of about 3/32" andV wherein the transverse width of `said slot is of the order of about I1/2.

4. The construction according to claim 3 wherein said enclosure for said resilient tube is of metal.

5. The construction according to claim 2 wherein said means attached to said tubular member -at the interior thereof includes a pair of `substantially rigid members extending inwardly of said tubular metal member and eX- tending toward each other.

References (lited in the file of this patent UNITED STATES PATENTS Trullinger et al Mar. 11, 1924 Murray Oct. 13, 1925 Cobi Apr. 11, 1939 Ruegg Apr. 9, 1940 Colvin Aug. 5, 1952 Chiverton May 29, 1956 Morris Aug. 26, 1958 Vos June 28, 1960 FOREIGN PATENTS France Nov. 14, 1949 

1. A CORE ASSEMBLY FOR DEFINING A DUCT THROUGHOUT THE LENGTH OF A CONCRETE SLAB DURING CASTING, SAID CORE ASSEMBLY HAVING A LENGTH GREAT IN COMPARISON TO ANY TRANSVERSE DIMENSIONS THEREOF, SAID CORE ASSEMBLY INCLUDING AN ELONGATED SLOTTED TUBULAR METAL MEMBER, SAID MEMBER BEING STRAIGHT AND LONG AND HAVING A TRANSVERSE SHAPE WHICH REMAINS UNIFORM THROUGHOUT THE ACTIVE LENGTH THEREOF AND IN TRANSVERSE SECTION DEFINES AN AREA WHICH IS ALMOST BUT NOT COMPLETELY SURROUNDED BY A SECTION OF SAID MEMBER SO THAT SAID MEMBER HAS A GENERALLY TUBULAR SHAPE WITH A SLOT EXTENDING THE FULL LENGTH THEREOF, A MOULDING COVERING SAID SLOT AND TENDING TO KEEP SAID SLOT CLOSED EVEN THOUGH THE SLOT WIDTH IS INCREASED BY DEFORMING SAID MEMBER, AN AIRTIGHT, FLEXIBLE TUBE WITHIN SAID MEMBER AND HAVING THE PROPERTY OF LATERAL EXPANSION IN RESPONSE TO FLUID PRESSURE, AND LATERALLY EXPANDABLE MEANS DISPOSED OVER SAID FLEXIBLE TUBE AND COUPLED TO SAID SLOTTED TUBULAR MEMBER ONLY AT REGIONS ADJACENT THE SLOT, SAID AIR-TIGHT 